The present invention relates to a material handling device and more particularly relates to a material handling system used in a plotter which draws graphic information on both a sheet of plotting material as well as on an underlying carbonized sheet.
It is generally known to use in a plotter rolls of carbon sheet material and plotting sheet material and to orient the respective sheets of material such that the carbonized surface of the carbon sheet upwardly faces and underlies an overlying sheet of the plotting material whereby a mechanical plotting instrument is pressed downwardly against the plotting sheet to inscribe graphic information on its surface and to transfer to the underside of the plotting material sheet a carbon imprint of this information. U.S. Pat. No. 4,512,079 issued on Apr. 23, 1985, and U.S. Pat. No. 4,400,704, issued on Aug. 23, 1983 disclose plotters utilizing a sheet of plotting material which overlays a sheet of carbon material. In these patents, each sheet of material is a continuous strip of rolled stock which is separately advanced across a work surface during a plotting operation to provide fresh material to the work surface. However, in these devices, a common problem experienced during the plotting operation is the creation of an adherence force occurring between the underlying carbon sheet and the overlying plotting sheet due to the transfer of carbon from the carbon paper to the plotting sheet when downward pressure is exerted by the plotting instrument. Thus, means must be provided to separate the adhered sheet materials from one another after the imprint has been made.
In these previously known devices, the sheet of paper material is advanced in a line of travel which is orthogonal to the line of travel of the carbon sheet material. Separation, or the elimination of adherence between the sheet of carbon material and the sheet of plotting material is accomplished in some of these devices by continuously moving the sheet of carbon material relative to the sheet of plotting material as graphic information is simultaneously generated on the overlying sheet of plotting material. However, the carbon material is expensive and the continual advancement of the carbon material during the plotting operation is not cost effective and creates an increase in the job cost for each plotting operation. Alternatively, where the carbon paper is not continuously advanced in the previously known devices, the devices must employ mechanical separating means such as a wire or a blade or the like for separating the carbon material from the plotting material. Such separating means are subject to breakdown and contribute to an increased expense in the maintenance of the system because the blades and/or wires smear flaked carbon onto other machine parts.
Accordingly, it is an object of the present invention to provide a system which includes a plotting device employing a first sheet of plotting material and a second underlying sheet of carbon material which are advanced across a work surface from opposite ends of a work table and are capable of being separated from one another without continuous movement of the carbon material relative to the plotting material.
It is yet another object of the present invention to advance the sheet of plotting material in a first direction of flow and to advance the sheet of carbon material in a second opposite direction of flow to thereby create a separating movement between the two sheets of material.
Still another object of the present invention is to provide guide means which skew the line of travel of the sheet of carbon material relative to the line of travel to the sheet of plotting material such that imprints made on the carbon material are laterally shifted as well as being forwardly advanced relative to the sheet of plotting material by small advancing increments made to the carbon sheet material.
Still a further object of the present invention is to provide a system which efficiently utilizes a sheet of carbon material during a plotting operation.